John Korb wrote:
 
.. [snip]
 
           b^2 - 10*b
     c = ---------------
              60
 
The restated equation for "b" in terms of "c" is:
 
There are two solutions for "b", the above being a quadratic in "b".
 
   b = 5 + (1/2)(sqrt(240*c + 100))
and
   b = 5 - (1/2)(sqrt(240*c + 100))
 
You can choose the appropriate solution(s) in your case.
 
 
Kumar
HP CSY-India